The sealing of an enclosure can be tested using helium by inflating the enclosure with helium, by sucking in any helium which may escape via a possible leak using a sniffer, and then sending the flow of gas sucked in by the sniffer to a vacuum analyser which detects the presence of the tracer helium, if any, arriving at the analyser.
If the sniffer is located at a distance of several meters from the analyser, the response of the analyser is inconveniently delayed by a length of time which corresponds to the transit time required for the tracer helium to arrive at the analyser. One solution to this drawback has been to install an auxiliary pump connected in parallel to the sniffer gas circuit in order to move the tracer gas under viscous conditions at a reasonable speed. Such an auxiliary pump is generally installed near to the analyser. Unfortunately this method has the drawback of requiring extra pumping apparatus, for example a membrane pump or a vane pump. This makes the detector more bulky and also requires an auxiliary source of power to drive the auxiliary pump.